Vehicles having lifting cranes or elevated work platforms or baskets mounted on the vehicle chassis commonly have one or more stabilizer actuators mounted on opposite sides of the vehicle, with each stabilizer actuator having a ground-engaging foot to prevent the vehicle chassis from capsizing during operation of the crane or other elevated work station. It is important that the part of the hydraulic circuit used to operate the crane or work station be isolated to assure that the work station cannot be elevated relative to the vehicle chassis unless the stabilizer actuators are in operative position and functioning to prevent tipping or capsizing of the vehicle chassis.
Known methods to accomplish the aforesaid isolation have either been a combination of electrical limit switches and solenoid-operated hydraulic valves or cam-operated hydraulic valves. In both of these methods, the sensing of the proper positioning of the stabilizer actuator is triggered by motion of a piston rod of the stabilizer actuator past a fixed position on the vehicle chassis. As a result, when the vehicle is on uneven or nonlevel ground, or when one side of the vehicle is adjacent to a paving curb or similar elevation, the operation of a limit switch or a cam-operated valve may be prevented because the ground-engaging foot may contact the ground before passing the fixed-position trigger point. Conversely, if there is a hole in the ground at the location where a ground-engaging foot attempts to make contact with the ground, there can be operation of a limit switch or cam-operated valve, even though the ground-engaging foot has not been placed in firm engagement with the ground.